The various modifications of aluminum hydroxides have widespread commercial applications. For example aluminum hydroxides are useful as flame retardants, filter media, reinforcement fillers in plastics and adhesives, filler pigments, catalysts, ingredients of paper coatings, catalyst supports, precursors for the production of activated alumina, and as raw materials for the production of aluminum.
The best defined crystalline forms of aluminum hydroxides are the trihydroxides, Al(OH)3, including gibbsite, bayerite, and nordstrandite; and two modifications of aluminum oxide hydroxide, AlO(OH): boehmite (γ-aluminum oxide hydroxide) and diaspore (α-aluminum oxide hydroxide). Moreover, methods of producing fibrous forms of aluminum hydroxides are known in the art. For example, U.S. Pat. No. 2,915,475 to Bugosh discloses fibrous alumina in the form of fibrils having an average length in the range from 100 to 700 millimicrons, the remaining average dimensions being in the range from 3 to 10 millimicrons, the axial ratio being from 50:1 to 150:1, and the product having the following physical properties: surface area 250 to 350 m2/g, X-ray of boehmite and the ratio of peak intensities of the product to boehmite of a surface of less than 10 m2/g at the 020 crystal lattice plane being less than 40:100.
U.S. Pat. No. 3,031,417 Wilkinson discloses a process for making fibrous alumina monohydrate aquasols comprising the steps of mixing a solution of alum with a solution of a soluble carbonate while maintaining a mole ratio of carbonate ions to aluminum of from about 1.50 to 1.90 so as to form carbonated, hydrated alumina gel having an activity, θ, such that the time in minutes required to depolymerize one-half of a sample of such gel in excess 0.50 N acetic acid at 30° C. is less than, 300 minutes, washing the gel with water until the gel contains a mole ratio of sulfate ions to aluminum of less than about 0.01:1 and a mole ratio of cations to aluminum of less than about 0.04:1, mixing the gel with a weak monobasic organic acid selected from the group consisting of acetic and formic acid so as to obtain an initial concentration of 5 to 10% Al2O3 and a mole ratio of aluminum to acid anion of from about 0.50:1 to 4.0:1, and heating the mixture of gel and acid under autogenous pressure to from about 140 to 180° C. for from about 10 minutes to 7 hours. The '417 patent further teaches that X-ray diffraction of the fibrils discloses that they have the X-ray diffraction of boehmite.
U.S. Pat. No. 6,838,005 B2 to Tepper et al. discloses a method of making a non-woven electropositive filler, the method comprising obtaining an aluminum source; reacting said aluminum source in an aqueous solution at a temperature sufficient to form non-spherical nano alumina particles; mixing the non-spherical nano alumina particles with a second solid, wherein mixing is effected substantially simultaneously with reacting so that the aluminum source is reacted in the presence of the second solid. The '005 patent also teaches the fibers are comprised of alumina, with various contents of combined water to result in compositions of pure Al(OH)3 or AlO(OH), or mixtures of the two, with possible impurities of gamma and alpha alumina.
Although the aforementioned references disclose fibrous forms of aluminum trihydroxide, Al(OH)3, and the modification of aluminum oxide hydroxide, AlO(OH), known as boehmite, they do not teach or suggest an aluminum oxide dispersion comprising a solvent and aluminum oxide nanofibers suspended in the solvent, wherein the nanofibers comprise from 0 to 99.99% (w/w) of γ-AlO(OH) and from 0.01 to 100% (w/w) of γ-Al2O3.